Safety plug for electrical devices



Fel). 3, W. E Cox SAFETY PLUG FOR ELECTRICAL DEVICES 2 sheets-sheet 1 Filed May 17, 1968 INVE NTOR WILLIAM E. COX

BY d W7 ATTORNEYS Feb. 3, 1970 w. E. cox 3,493,915 SAFETY PLUG Fon ELECTRICAL DEVICES Filed May 17, 1968 2 Sheets-Sheet 2 INVENTOR WILLIAM E. COX

BY www ATTORNEYS Safes .Paterno U.S. Cl. 339-14 3 Claims .ABSTRACT 0F DISCLOSURE An 'electrical' plug is arranged to receive a jumper which can be inserted in and removed from the plug to connect and disconnect the plug from its attached cable.

. .A v Background of the invention uously: supervised-such as they are in a factory, persons unaware of the hazards-of such'tools may have access .to the tools. This is particularly true where there are ch11- dren who, lthrough curiosity,` attempt to operate an. electrical tool. Such operation may damage property or injure or kill a person. i Therefore, an object'of-my invention is to provide an improved safetyv'plug for electrical devices.

Another object of` my invention is'to provide an 1mproved safety plug that requires insertion of a jumperun order that the plug Acan 'supply'.electricity to a devrce connected to .the plug; A 1 'f f -Y Another object of myinvention .is to provide animproved safety plug and'jumperfwhich have reduced .or minimized 'exposure of live electrical contacts either with the jumper in operative posftionforwi'th the jumper removed.

Summary of thel invention Briefly, these and other objects are achieved in accordtrically insulating' materiali vThe body has first and second generally at surfacesthat are yspaced and parallel. Fl'rst and second conductive circuit prongs and a conductlve ground plug extend from the, first ,'surface, and first and Ice claims. The structure and operation of my invention, together with further objects and advantages, may be better understood from the following description given in connection with the accompanying drawing, in which:

FIGURE 1 shows a perspective view of a preferred embodiment of my improved safety plug and jumper; and

FIGURES 2 and 3 show cross sectional views taken along the line 2-2 and the line 3-3 respectively in FIGURE 1.

Description of the preferred embodiment In FIGURE l, I have shown a perspective view of a safety-plug l() and a jumper 11 in accordance with my invention. Both the plug 10 and the jumper 11 are preferably made of a resilient, electrically insulating material such as molda-ble natural or synthetic rubber. The plug 10 is intended to be used with a conventional 115 volt outlet having two live sockets and a ground socket. The plug 10 is provided with two flat surfaces 13, 14 which are spaced and preferably parallel to each other. Two conductive prongs 15, 16 and a ground prong 17 extend outwardly from the surface 13 in a configuration that corresponds to theconfiguration of a standard electrical outlet. As is typical, the conductive prongs 15, 16 are of the flat blade type, and the ground prong 17 is of the round type. A cable or cord 19 extends from another face 20 of the plug 10. The cable or cord 19 has three insulated conductors 21, 22, 23 which are connected to an electrical appliance or tool at the endl of the cable 19.

With reference to FIGURES 2 and 3, which are taken along the line 2-2 and the line 3-3 respectively, I have shown the internal configuration and construction of the plug 10 and the jumper 11. FIGURE 2 Shows the jumper 11 removed from the plug 10, and FIGURE 3 shows the jumper 11 inserted into the plug 10. With particular reference to FIGURE 2,the plug 10 is provided with first and ,second holes 25, 26. I prefer that the holes 25, 26 have a different spacing relative to the prongs 15, 16 so that the jumper 11 will not accidentally be inserted in an electrical outlet and create a short circuit.

v These holes 25, 26 extend from the surface 14 inwardly second jumper sockets yare'positioned in the second surface of the plug body. Means are provided within the plug body for electrically connectingthe first circuit prong to the first socket. A cable having three conductors extends -from the plug body. Means are provided within the plug body for electrically connecting the second clrcult prong, the ground prong, and the second socket to the three cable conductors. A jumper is formed of electrically insulating material and has a flat surface from which' two conductive jumper prongs extend. The jumper prongs are connected together within the jumper body. When the cable is to be energized, the jumper prongs are inserted into'vthe jumper sockets to close the electrical circuit from the first conductive prong to its respective cable conductor. When the electrical circuit is to be de-energized, the jumper prongs are removed from the plug body. The sockets are positioned sufiiciently far inside of the plug body so that live electrical contacts are inaccessible.

Brief description of the drawing toward the surface 13. At the bottom of each of the holes 25, 26 is an electrically conductive socket or terminal 25a, 26a. The conductive socket 25a is connected to the first prong 15 through a suitable wire or piece 27. Or, the

ance with my invention by a plug body formed of elec- L conductive socket 25a, the piece 27, and the prong'15 may be formed integrally. The other conductive socket 26a is connected to the first conductor 21 in the cable 19 by crimping or other suitable means. The second prong 16 is connected to the second conductor 22 in the cable 19 by` crimping or` other suitable means. As shown in IFIGURE 2, the conductiveprongs 15, 16. may be provided with suitable projections or lextensions 15a, 16a to hold the prongs 15, 16 more firmly in the plug 10.

The jumper 11 is provided with a fiat surface 30 from which two conductive jumper prongs 31, 32 extend in insulated relation. The jumper prongs 31, 32 are configured to correspond to the positions of the conductive sockets 25a, 26a, and hence can not be inserted in an electrical outlet. The jumper prongs 31, 32 are interconnected by any suitable means, such as a metallic strip 33 which is positioned within the jumper 11, or which may be formed integrally with the prongs 31, 32. The other surfaces of the jumper 11 may be provided with ridges 11a as shown in FIGURE 1 in order to facilitate grasping of the jumper 11.

With reference to FIGURE 3, I have shown the jumper 11 in its inserted position in the plug 10. The connection of the ground prong 17 to the third conductor 23 in the cable 19 is also shown, and is made by crimping or other suitable means. As indicated by the dashed lines in FIG- URE 3, when the jumper 11 is inserted into the plug 10,

its prongs 31, 32 engage the conductive sockets 25a, 26a respectively. This provides an operative electrical circuit from the conductive prong 15 through the jumper 11 to the first conductor 21 in the cable 19. Hence, the three conductors 21, 22, 23 in the cable 19 are respectively connected to the prongs 15, 16, 17.

When the electrical appliance or tool on the cable 19 is to be rendered inoperative, the jumper 11 is removed. Even though the plug is inserted into an electrical outlet, there is no operative or energizing connection between the prong 15 and the first cable conductor 21. Hence, the tool or appliance can not be operated by a person having no electrical knowledge or by a child. And, the conductive sockets 25a, 26a are positioned sufficiently far inside of the plug 10 so that they can not be accidentally touched by a person or a piece of metal.

My improved safety plug and jumper are not only safe and reliable in their operation, but they are also relatively easy to construct. The jumper 11 can be formed by assembling the prongs 31, 32 and the connecting strip 33, and then molding the jumper 11 around the assembled prongs 31, 32 and the strip 33. Likewise, the plug 10 can be molded around the prongs 15, 16 when connected to the conductive sockets 25a, 26a. The prongs 15, 16, 17 and the the sockets 25a, 26a can be held in the proper position by a suitable jig or fixture.

It will thus be seen that my invention provides a new and improved safety plug and jumper. While I have shown only one embodiment of my safety plug and jumper, persons skilled in the art will appreciate that modifications may be made. For example, another set of jumper prongs and conductive sockets may be provided for the plug prong 16, so that both sides of the electrical circuit can be broken. This is particularly desirable if there is no third ground wire. The conductive sockets may be cylindrical in shape, as shown, or may have other shapes. Therefore, while my invention has been described with reference to a particular embodiment, it is to be under- 4 stood that modifications may be made without departing from the spirit of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An improved safety plug and jumper for electrical devices, comprising:

(a) a plug body formed of electrically insulating material, said body having first and second generally flat surfaces that are spaced apart and that are generally parallel to each other;

(b) first and second conductive circuit prongs and a conductive ground prong positioned in a spaced, insulated relation in said plug body, said conductive prongs extending from said first flat surface in a configuration that corresponds to an electrical outlet;

(c) said plug body having rst and second jumper holes formed in a spaced, insulated relation in said plug body, each of said jumper holes having an'insulated opening formed in said plug body at said second flat surface and extending into said plug body;

(d) first and second conductive sockets respectively positioned in saidV first, and second jumper holes within said plug body and spaced v,from said second flat surface; t l

(e) means within said plug body for electrically connecting said first circuit prong to said first conductive socket; v

(f) cable means comprising three insulated conductors extending from said plug body at another surface thereof;

(g) means within said plug body for electrically connecting said second circuit prong, said ground prong, and said second conductive socket to said three cabl conductive respectively; t

(h) a jumper b odyformed of electrically insulating material, said jumper body having at least one generally flat surface;

(i) first and second conductive jumper prongs positioned in a spaced, insulated relation in said jumper body, said jumper prongs extending from said flat surface in a configuration that corresponds to said rst and second conductive jumper sockets;

(j) and means within said jumper body for electrically connecting said first and second jumper prongs together, whereby said jumper prongs can be inserted into and removed from said first and second conductive jumper sockets to effectively connect and disconnect said first circuit prong and its respective cable conductor.

2. The improved safety plug and jumper of claim 1 wherein said plug body and said jumper body are respectively formed of integral molded resilient material.

3. The improved safety plug and jumper of claim 1 wherein said first and second conductive jumper sockets and said first and second conductive circuit prongs have different spacings.

References Cited UNITED STATES PATENTS 3,140,908 7/1964 McCutcheon 339-19 3,242,455 3/1966 Horvath et al. 339-14 FOREIGN PATENTS 802,822 2/1951 Germany. 1,119,368 12/1961 Germany.

532,429 8/ 1955 Italy.

MARVIN A. CHAMPION, Primary Eitaminer P. A. CLIFFORD, Assistant `Examiner vU.s. c1. X11. 'l 339-19, 166

ggg l UNITED STATES PATENT OFFICE I CERTIFICATE OF CORRECTION Patent No. 3.493.915 Dated 'p February 3, 1970 -Invent:or.(s) f W. E Cox It is certified that error appearsy in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim l, subparagraph (g) line "conductive" should be conductors n. (Specification Claim l, subparagraph (g) line 3) Signed and sealed this 30th day of Mar-ch 1971.

(SEAL) Attest:

EDWABD.M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR. Attestlng Officer Commissioner of* Patents 

